The present invention relates to a device for measuring a thickness of sheet articles.
In device for transporting sheet articles, especially X-ray sheet film loading and unloading devices, a sheet article is moved along a transportation path by a suitable transporting roller pair. In X-ray sheet film loading and unloading devices, the X-ray sheet film is removed from the magazine, transferred to a transporting roller pair, and transported from it to a further transporting roller pair and so on until theX-ray sheet film is transported to a cassette to be loaded and placed in it. The transporting rollers can be formed as complete rollers or as roller pieces mounted on a shaft. An X-ray sheet film cassette must be loaded during this process only with an X-ray sheet film. It is however necessary to detect double and multiple films so as to prevent their transportation. In order to solve this problem of the detection of the double and multiple films several devices are proposed in the prior art.
One of the possibilities is the utilization of infrared light barriers. The presumption for this method is that the light permeability reduces when two or more X-ray sheet films lie over one another. When in a constant time interval the passing light quantity is integrated, a value is produced which is dependent on the number of the X-ray sheet films located in the region of the through light barrier. This arrangement however cannot be used for infrared-sensitive X-ray sheet film or X-ray sheet film with high transparency. German document DE-OS 3,800,249 discloses an X-ray sheet film loading and unloading device, in which a transporting roller of one transporting roller pair is turnably supported on a lever arm about a lever point. The second lever arm which is located opposite the lever arm with the transporting roller is arranged under a spring force, so that the rollers of the transporting roller pair are pressed against one another. When an X-ray sheet film is drawn from this transporting roller pair, the transporting roller supported on the lever is turned depending on the number of the drawn film sheets. The second lever arm is also turned in correspondence with the lever condition and actuates a microswitch when more than one X-ray sheet film is drawn by the transporting roller pair. This means that it can be no difference whether one or no X-ray sheet film is drawn by the transporting rollers. The arrangement for measuring the X-ray sheet film thickness disclosed in this document also has a further disadvantage in that it is mechanically very expensive, since a transporting roller must be supported turnably and it is very tolerance sensitive, with respect to the roller diameter, roller elasticity, lever size, position of the opening for the lever and roller support, etc. In addition, there is a danger that the once adjusted arrangement can lose the adjustment due to the transporting movement and the vibrations during certain times. Thereby, no reliable detection of the multiple sheets or films can be guaranteed over a long time.